Step support for SliderIOS

Summary: Add step support to SliderIOS
Closes https://github.com/facebook/react-native/pull/3746

Reviewed By: svcscm

Differential Revision: D2595360

Pulled By: nicklockwood

fb-gh-sync-id: 4adf8bcdf46c709776d779244ba3de2b40eb27d6

Libraries/Components/SliderIOS/SliderIOS.ios.js

@@ -41,6 +41,13 @@ var SliderIOS = React.createClass({
      */
     value: PropTypes.number,
 
+    /**
+     * Step value of the slider. The value should be
+     * between 0 and (maximumValue - minimumValue).
+     * Default value is 0.
+     */
+    step: PropTypes.number,
+
     /**
      * Initial minimum value of the slider. Default value is 0.
      */
@@ -103,6 +110,7 @@ var SliderIOS = React.createClass({
       <RCTSlider
         style={[styles.slider, this.props.style]}
         value={this.props.value}
+        step={this.props.step}
         maximumValue={this.props.maximumValue}
         minimumValue={this.props.minimumValue}
         minimumTrackTintColor={this.props.minimumTrackTintColor}

React/Views/RCTSlider.h

@@ -14,5 +14,7 @@
 @interface RCTSlider : UISlider
 
 @property (nonatomic, copy) RCTBubblingEventBlock onChange;
+@property (nonatomic, assign) float step;
+@property (nonatomic, assign) float lastValue;
 
 @end

React/Views/RCTSliderManager.m

@@ -30,12 +30,30 @@ RCT_EXPORT_MODULE()
 
 static void RCTSendSliderEvent(RCTSlider *sender, BOOL continuous)
 {
-  if (sender.onChange) {
+  float value = sender.value;
+
+  if (sender.step > 0 &&
+      sender.step <= (sender.maximumValue - sender.minimumValue)) {
+    value =
+      MAX(sender.minimumValue,
+        MIN(sender.maximumValue,
+          sender.minimumValue + round((sender.value - sender.minimumValue) / sender.step) * sender.step
+        )
+      );
+  }
+
+  if (!continuous) {
+    sender.value = value;
+  }
+
+  if (sender.onChange && (sender.lastValue != value || !continuous)) {
     sender.onChange(@{
-      @"value": @(sender.value),
+      @"value": @(value),
       @"continuous": @(continuous),
     });
   }
+
+  sender.lastValue = value;
 }
 
 - (void)sliderValueChanged:(RCTSlider *)sender
@@ -49,6 +67,7 @@ static void RCTSendSliderEvent(RCTSlider *sender, BOOL continuous)
 }
 
 RCT_EXPORT_VIEW_PROPERTY(value, float);
+RCT_EXPORT_VIEW_PROPERTY(step, float);
 RCT_EXPORT_VIEW_PROPERTY(minimumValue, float);
 RCT_EXPORT_VIEW_PROPERTY(maximumValue, float);
 RCT_EXPORT_VIEW_PROPERTY(minimumTrackTintColor, UIColor);